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0 a <br /> 4.0 WORK PLAN TO DECOMMISSION EIGHT WELLS <br /> In a letter to PG&E, the DTSC (2004) approved the decommissioning of eight existing <br /> groundwater monitoring wells at the Site and requested the submittal of a well- <br /> decommissioning work plan. <br /> Existing Well Construction <br /> The construction details of the eight wells are summarized in Table 1. Of these wells, <br /> four are completed in the A zone (MW-1 R, MW-2, MW-3, and MW-11), two in the B <br /> zone (MW-1 D and MW-17), and two in the C zone (MW-15 and MW-16). <br /> Pre-Field Logistics <br /> Encroachment permits will be obtained from the City of Stockton. The City permits, this <br /> work plan, and DTSC approval of this work plan will be submitted as an application to <br /> the County for permits to decommission the wells. After the County issues permits and <br /> before field decommissioning activities, Underground Service Alert will be notified for <br /> utility clearance. ENV America personnel will follow the health and safety procedures <br /> described in the Site Health and Safety Plan (included as Exhibit A) during field <br /> activities at the Site. <br /> Well Decommissioning Plan <br /> The County requires that groundwater monitoring wells be destroyed by over-drilling <br /> and subsequently backfilling with a cement slurry via a tremie pipe from the bottom of <br /> the borehole to ground surface. Based on the total depths of the wells, the A- and B- <br /> zone wells will be decommissioned using a drill rig equipped with hollow-stem augers, <br /> and the C-zone wells will be decommissioned using the mud-rotary drilling method <br /> (Table 1). The boreholes will be backfilled with neat bentonite-cement slurry via a tremie <br /> pipe from the bottom of the boreholes to the ground surface. <br /> Waste Materials <br /> The drilling mud, soil cuttings, and well construction debris generated from the well <br /> decommissioning activities will be contained in roll-off bins and temporarily placed within <br /> the PG&E property. The materials will be profiled and subsequently transported for off- <br /> site disposal at an appropriate facility. <br /> 11 ENV. <br /> A M E A 1 C A <br /> P\PG&E\PGE-05-01 Stockton MW26R In esGgaoco\MW26 Work Plan\PGE Stockton MW26R WPdoc <br />